<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text">
<input type="button" value="平方" onclick="f()">
<input type="button" value="求和" onclick="f1()">
<div>结果:</div>
<script>
  let i = document.querySelector("input")
  let d = document.querySelector("div")
  function f() {
    if (isNaN(i.value)){
      d.innerText="输入有误!"
      return;
    }
    d.innerText ="结果:"+ i.value*i.value
  }
  function f1() {
   //d.innerText="结果:"+(parseFloat(i.value)+parseFloat(i.value))
    d.innerText = "结果:"+(i.value*1+i.value*1)
  }
</script>
</body>
</html>